Deep venous thrombosis (DVT) is a significant clinical problem that can also lead to potentially fatal pulmonary embolism. Clinical studies reveal that thrombus resolution is central to the pathogenesis of post- thrombotic syndrome. Mechanisms that lead to thrombus resolution in DVT are not well understood at this time. It is clear, however, that optimal resolution of the thrombus requires an inflammatory response in which neutrophil and macrophages are recruited to the thrombus, and require proteases to degrade the matrix and thrombus. Our preliminary data employing mouse models of DVT reveal that genetic deletion of the LDLr results in enhanced thrombus resolution in mouse models of DVT. This appears to result from early recruitment of macrophages into the lesion in LDLr-deficient mice. This is accompanied by increased expression of MMP2; a protease implicated in thrombus resolution and decreased expression of PAI-1 in the thrombus isolated from LDLr-deficient mice. Further, we discovered that mice in which the LRP1 gene has been selectively deleted in macrophages also demonstrate enhanced thrombus resolution in a model of deep vein thrombosis. The central hypothesis of this application is that certain LDL receptor family members play important roles in modulating inflammatory events and protease activity thereby regulating clot resolution in mouse models of Deep Vein Thrombosis (DVT). The specific hypotheses to be tested are: 1) that the LDLr modulates thrombus resolution during DVT by modulating inflammation; 2) that LRP1 modulate thrombus resolution by regulating protease levels and by regulating signaling events in inflammation and 3) that we can engineer inhibitor molecules for receptor blockade that would enhance thrombus resolution in DVT. These hypotheses will be tested in the following specific aims: 1) Determine mechanisms by which the LDLr regulates thrombus resolution in mouse models of DVT; 2) Define the mechanisms by which LRP1 expressed in macrophages modulates thrombus resolution in mouse models of DVT and 3) Develop strategies for receptor blockade by designing antagonists for LDLR and LRP1 to enhance thrombus resolution in DVT. PUBLIC HEALTH RELEVANCE: Deep vein thrombosis (DVT) and resulting pulmonary embolism represents a significant clinical problem. Clinical studies reveal that rapid resolution o the thrombus is a critical factor for patient outcomes. Those patients whose thrombus resolves slowly often experience damage to the veins. We have discovered two new molecules, the LDL receptor and LRP1 that modulate thrombus resolution in mouse models. These studies will identify new mechanisms that modulate this process, and will allow us to develop new strategies for potential therapeutic intervention in this disease.